How about High Voltage fuse for Motor protection?


The SIBA HHM fuselinks all requirements according IEC
60644 “Specification for highvoltage fuselinks for motor
circuit application”.
The special characteristic allows a full short circuit
protection for the motor circuit components as well as
a withstand capability for starting inrush currents and
cyclic current impulses. Application
guideline:
The suitable rated current of the fuselink is mainly
determined by two important parameters:
·the inrushcurrent during the runup period of the motor
due to high magnetizingcurrents
·to create less heating in the enclosure
For general, the inrush current can be calculated as five
to six times rated current of the motor.
For practical use the runup time of different motor types
are separated into three main categories:
Table 1:runup times

example
of motor type 

pumpmotor 
millmotor 
fanmotor 

To avoid any aging due to frequent switchingoperations
following deratingcoefficients have to taken into account:
Table 2:deratingcoefficients
Note: Two immediate successive starts are admissible.
Selectionprocedure:
· determine the inrushcurrent (individually
given, or multiply the normal operating of the motor
by 6) and divide it by the corresponding deratingcoefficient
of table 2,considering the quantity of starts per
hour
· transfer this value to the Xaxis of the time
current characteristic of the fuselink
· mark the crossingpoint of these Xand Yvaluse

The time current curve of the fuselink, which is directly
placed on the right side next to the marked point, reflects
the correct rated current of the fuselink have to be
chosen.This rated current of the fuselink must at least
1.3 times of the normal operating current of the motor.
In other cases the next higher rated current has to be
taken.
The abovementioned procedure is valid for directstaring
motors as well as for assistedstarting. In this case
the calculated inrush current is decreased and a smaller
rated current of the fuselink could be chosen as in case
of directstarting.
For such applications an inadmissible temperature increase
must be avoided by a rated current of the fuselink higher
or equal to 1.3 times normal operating current of the
motor.

